Despite the great promise, magnetic nanoparticle hyperthermia (mNHP) has had limited success in clinical applications. This limited success is due, in part, to technical difficulties of selective heat delivery to the target tissue without overheating adjacent normal tissue. Magnetic nanoparticle hyperthermia for cancer therapy is an application of alternating magnetic fields (AMFs) in which magnetic nanoparticle heating depends upon both AMF frequency and amplitude (Jordan et al., 1997; Rosensweig, 2002; Bordelon et al., 2011). Generally, the objective is to develop nanoparticle and AMF device combinations that produce a maximum particle-associated heating rate, or loss power for a given flux (peak-to-peak) magnetic field. For many magnetic materials, the loss power increases both with increasing AMF frequency and amplitude, thus motivating development of particles that generate therapeutic heating with safe AMF exposure. For a given magnetic ion oxide nanoparticle (MION) formulation localized in tissue, the amount of heat deposited during mNHP depends on both the intratumoral iron-oxide nanoparticle (IONP) concentration and AMF parameters.
When a region of tissue in an animal or a patient is subjected to alternating magnetic field (AMF), non-specific Joule heat is deposited into the tissue due to eddy currents. The total non-specific power deposited is proportional to H2f2r2; where H and f are AMF amplitude and frequency, and r is the radius of the eddy current path, which is related to the radius of tissue exposed to AMF. For most iron-oxide nanoparticles (IONPs) the heat generating ability is proportional to H2f Hence, lower AMF frequencies in the range of 100 kHz to 400 kHz are typically used in mNPH applications (Atkinson et al., 1984). For mNPH to be effective, the IONPs should generate higher heating at low field amplitude, or H-values.